This invention relates to knotters, i.e. mechanisms for tying knots, for any application but for convenience, the invention will be discussed in relation to agricultural baling machines in which bales of hay or straw, for example, are formed and secured by flexible material in which knots are tied by a knotter.
In conventional crop balers, hay, straw and similar crop material that has been previously cut, windrowed or swathed, is picked up from the ground by a pick-up unit and fed in successive batches or charges into an elongated bale chamber in timed sequence with a reciprocating plunger. The plunger compresses the material into bales and, at the same time, gradually advances the bales towards the outlet of the bale chamber. As the bales reach a predetermined length, as determined by a metering device, a knotter is actuated which wraps cord, twine or other flexible tie material around the bale and secures the ends of the material together.
In a typical baler a knotter is mounted on the bale chamber above a slot therein, the knotter comprising a twine holder from which twine extends to encircle a bale. During the baling operation, the leading strand of twine is held by the twine holder and extends forwardly across a twine retainer finger and a billhook and then in front of the bale. The twine retainer finger supports the stand so that it does not bear forcefully against the billhook. A needle is involved in completing the encirclement of twine around the bale and when advancing, the needle lays a trailing strand across the twine retainer finger, billhook and twine holder. A twine finger captures these strands of twine and positively positions the stands against the heel of the billhook. Thus, there is presented in a certain zone a pair of twine portions or stands lying alongside each other and these portions are twisted into a bight by the billhook and a portion thereof is pulled through the bight to form a double overhand knot. On completion of the operation of the knotter, the twine finger returns to the initial position. The removal of the tied knot from the billhook involves mechanical stripping by a movable member which normally embodies a knife operable to cut the twine from the twine supply so that the tied bale is complete in itself. The tying mechanism thus includes several components working in a precisely timed relationship so that theoretically the mechanism ties one knot for each bale and prepares the twine for the succeeding bale.
A knotter is inherently a relatively complicated structure, and the precisely timed operation thereof suffers at times from faulty operation. This may be due to the vibrations of the baler, the tension in the twine and the jarring of the baler as it moves through the field. The crop may be tough or resilient causing the strands of twine to jump about. Variations in the baling twine also affect the knotting operation. Balers are operated, and often parked, in a field, whereby the knotter is exposed to all weather conditions. Also, the knotter is subjected to dirt, crop and debris resulting in abrasion and interference of operation.
An improved knotter is disclosed in U.S. Pat. No. 4,161,097 issued July 17, 1979 and this has been found to exhibit exceptional structural simplicity and highly reliable operational characteristics. However, this improved knotter suffers some disadvantages, one of which is that it employs a fixed knife for cutting the twine at a predetermined point in the operation of the knotter with the result that the twine is cut substantially at the same point on the knife edge which thus becomes blunt comparatively quickly and tends to produce ragged knot ends which may adversely affect the ensuing knot. Also, if the twine is only partially cut, the operation of the knotter can be impaired. A similar problem occurs with the knife mounted for movement with the knot-stripping member of earlier knotters.